Mask used in charged particle beam projecting apparatus and method for dividing pattern

ABSTRACT

A method for dividing a pattern according to the present invention is used in a charged particle beam projecting apparatus, in which: a plurality of block patterns into which a projected pattern to be projected on a substrate is divided are respectively formed in a plurality of regions of a mask; the plurality of regions of the mask are successively irradiated with a charged particle beam so that the block patterns are successively projected on the substrate; and as a result the projected pattern is formed on the substrate. The method includes a step of dividing the projected pattern into the block patterns by parting lines which are plotted in accordance with profiles of pattern elements that constitute the projected pattern when the block patterns are determined.

This is a divisional of application Ser. No. 08/720,019, filed Sep. 27,1996 pending.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a mask used in a charged particle beamprojecting apparatus adapted to project respective patterns of aplurality of regions, formed in a mask, on a substrate by means of acharged particle beam, so as to project a desired pattern on thesubstrate. This invention is also concerned with a method for dividingthe pattern to be projected on the substrate.

2. Description of Related Art

A known lithography apparatus for forming an integrated circuit patternon a semiconductor wafer comprises a charged particle beam projectingapparatus wherein a mask having a certain pattern formed therein isirradiated with a charged particle beam, such as an electron beam, and aportion of the pattern in the irradiated range of the mask is projectedin a reduced ratio on the wafer by means of a projecting lens. In thistype of projecting apparatus, the entire area of the mask cannot besimultaneously irradiated with the charged particle beam, and thereforethe field of view of an optical system is divided into a multiplicity ofsmall regions, so as to project a pattern image that is also dividedinto small sections. Such an apparatus is disclosed, for example, inU.S. Pat. No. 5,260,151.

FIGS. 5A and 5B are perspective views schematically showing therelationship between a pattern of a mask 1 to be projected, and apattern projected on a wafer 2. The appearance of the wafer 2 as a wholeis shown in FIG. 5A, and a "Va" region of this wafer 2 is shown inenlargement in FIG. 5B. As shown in FIG. 5B, the mask 1 has a pluralityof rectangular small regions 1a, and a boundary region 1b that providespartition in a grid form for defining these small regions 1a. In each ofthe small regions 1a of the mask 1, there is formed a section of apattern (which will be described later) to be projected on a region 2aof the wafer 2 that corresponds to one chip (one piece ofsemiconductor). The boundary region 1b is formed uniformly of a materialthat interrupts or largely scatters the charged particles of theincident beam. The charged particle beam is formed into a crosssectional shape (rectangular shape) similar to that of the small region1a, and is directed at one of the small regions 1a of the mask 1 bymeans of a deflector for selecting the field of view (not shown). Thecharged particle beam BM that has passed the small region 1a passes acrossover CO on an optical axis AX by means of a projecting lens (notshown), and is incident upon a unit region 2b within a chip region 2a ofthe wafer 2. In this manner, the image of the pattern formed in thesmall region 1a of the mask 1 is projected in a reduced ratio on theunit region 2b of the wafer 2.

FIG. 6A shows a part of a pattern 3 to be projected on the wafer 2, andFIG. 6B shows a part of a mask pattern formed in some of the smallregions 1a of the mask 1. The pattern 3 consists of pattern elementsP11, P12 . . . , and is divided by parting lines d1 indicated by dashedlines into a plurality of block patterns 3aa, 3ab . . . which are to beprojected on the wafer 2. On the other hand, small regions 1aa, 1ab . .. of the mask 1 are identical with the small regions 1a shown in FIG.5B. The pattern elements included in the block pattern 3aa are formed inthe small region 1aa of the mask 1, and the pattern elements included inthe block pattern 3ab are formed in the small region 1ab.Conventionally, the pattern 3 is routinely divided into the rectangularblock patterns 3aa, 3ab . . . , as shown in FIG. 6A and FIG. 6B,irrespective of the shape of the pattern elements P11, P12 . . . of thepattern 3.

With the pattern 3 routinely divided into the block patterns asdescribed above, some of the pattern elements intersect the partinglines such that each of these intersecting pattern elements extends overtwo block patterns. For example, the pattern element P22 intersects theparting line d1 of the projected pattern 3, and is thus included in bothof the block patterns 3aa and 3ab, as shown in FIG. 6A, so that theelement P22 is split into two pattern elements P22a, P22b that arerespectively formed in the small regions 1aa and 1ab of the mask 1, asshown in FIG. 6B. Since the pattern element P22 is projected onto thewafer 2 by respectively projecting the pattern elements P22a, P22b, aconnecting portion on the wafer 2 between these pattern elements P22a,P22b inevitably suffers from connection error. If the pattern elementP22 corresponds to a drain layer of a MOS transistor, for example, suchconnection error occurring in the wafer 2 may result in changes incharacteristics of the MOS transistor and reduced yield of the device.

Further, when the block patterns 3aa, 3ab are formed in the smallregions 1aa, 1ab of the mask, the area having z width where the blockpatterns 3aa, 3ab can not be formed is needed between the small regions1aa, 1ab to ensure the physical strength of the mask 1. If the size of asemiconductor device is assumed as 18×36 mm² and a size of the areacorresponding to one of the small regions of the mask is assumed as0.25×0.25 mm², a problem arises that the size of the mask becomes biggerso that longitudinal length increases by (72×z) and lateral lengthincreases by (144×z).

SUMMARY OF THE INVENTION

In a charged particle beam projecting apparatus wherein a pattern thatis divided into a plurality of regions is projected onto a substrate, itis an object of the present invention to provide a mask and a method fordividing a pattern to be projected, so as to reduce the connection erroroccurring in the projected pattern. And another object of the presentinvention is to provide a method for dividing a pattern to be projected,so as to minimize a size of a mask so that an optical system has lessload due to having a small sectional area of the beam and a drivingsystem of a mask stage has less load to move the mask on this maskstage.

The above first object may be accomplished according to one aspect ofthe present invention, which provides a method for dividing a patternused in a charged particle beam projecting apparatus, in which: apattern to be projected on a substrate is divided into a plurality ofblock patterns and the plurality of block patterns are respectivelyformed in a plurality of regions of a mask; the method comprising: astep of dividing the pattern into the block patterns by parting lineswhich are plotted so as to minimize intersecting pattern elements thatconstitute the pattern to be projected.

The above first object may also be accomplished according to anotheraspect of the present invention, which provides a mask used in a chargedparticle beam projecting apparatus for projecting a pattern, comprisinga plurality of regions in which a plurality of block patterns into whicha pattern to be projected on a substrate is divided are respectivelyformed, wherein: the pattern to be projected includes a plurality ofpattern elements; and the block patterns are produced by dividing thepattern to be projected by parting lines that are plotted so as tominimize intersecting of the pattern elements.

The above second object may be accomplished according to an aspect ofthe present invention, which provides a method for dividing a patternused in a charged particle beam projecting apparatus, in which: apattern to be projected on a substrate is divided into a plurality ofblock patterns and the plurality of block patterns are respectivelyformed in a plurality of regions of a mask; the method comprising: astep of detecting areas where pattern elements, which constitute theprojected pattern, do not exist in zones where parting lines can be set;a step of determining parting lines along with the areas; a step ofdividing the projected pattern into the block patterns by the determinedparting lines; and a step of forming the block patterns in the regionsof the mask while removing at least part of the areas so that the sizeof the regions is reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

This invention will be described in greater detail with reference tocertain preferred embodiments thereof and the accompanying drawings,wherein:

FIG. 1A is a view showing a part of a pattern of the first embodiment ofthe present invention;

FIG. 1B is a view showing a part of a mask of the first embodiment ofthe present invention;

FIG. 2 is a view showing irradiated regions at which a wafer isirradiated with a charged particle beam in the first embodiment of theinvention;

FIG. 3A is a view explaining a known example of a method for dividing apattern to be projected;

FIG. 3B is a view explaining an example of a method for dividing apattern to be projected according to the second embodiment of theinvention;

FIG. 4A is a view showing a part of a mask whose pattern is dividedaccording to the method of FIG. 3B;

FIG. 4B is a view showing irradiated regions at which a wafer isirradiated with a charged particle beam when the mask of FIG. 4A isused;

FIGS. 5A and 5B are perspective views showing the relationship between apattern of a mask when it is projected, and a pattern projected on awafer;

FIG. 6A is a view showing a part of a projected pattern that is dividedin a know method;

FIG. 6B is a part of a mask whose pattern is divided in a known method;

FIG. 7 is a schematic view showing the construction of the firstembodiment of the invention, which includes a deflector and others;

FIG. 8A is a view showing a part of a pattern of the third embodiment ofthe present invention;

FIG. 8B is a view showing a part of a mask of the third embodiment ofthe present invention; and

FIG. 8C is a view showing irradiated regions at which the wafer isirradiated with a charged particle beam in the third embodiment of thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

First Embodiment

FIGS. 1A and 1B are views showing a part of a pattern 3 to be projectedand a part of a mask 1, respectively, which are used in a chargedparticle beam projecting apparatus according to the first embodiment ofthe present invention. The pattern 3 to be projected of FIG. 1A has thesame pattern configuration as that of FIG. 6A, and the same referencenumbers as used in FIG. 6A are used in FIG. 1A to identify correspondingelements. The pattern 3 to be projected is divided by parting lines d2into a plurality of block patterns 3ba, 3bb . . . , and these partinglines d2 are plotted in a zigzag pattern so as not to intersect patternelements P11, P12 . . . . Namely, the parting lines d2 are bent at rightangles at appropriate points thereof so as to go between staggeredpattern elements P12, P22, P32 and P42, for example. The patternelements P11, P12, P21, P31, P32 and P41 included in the block pattern3ba are formed in the small region 1aa of the mask 1, and the patternelements P13, P22, P23, P33, P42 and P43 included in the block pattern3bb are formed in the small region 1ab of the mask 1.

Regions 4a, 4b defined by dashed lines in FIG. 1B represent irradiatedregions that are irradiated with a charged particle beam having auniform intensity. The irradiated regions 4a, 4b have boundaries thatare located outwardly of and spaced a predetermined dimension "x" fromboundaries of the small regions 1aa, 1ab of the mask 1. This dimension"x" is set to be smaller than the width of the boundary region 1b of themask 1.

FIG. 2 is a view showing irradiated regions at which a wafer 2 isirradiated with the charged particle beam. The charged particle beam isinitially incident upon the irradiated region 4a shown in FIG. 1B, and aportion of the beam that passes the mask 1 is then guided by aprojecting lens, deflector and others, so as to be incident upon theirradiated region 41a of the wafer 2. Thus, an image of the patternelements P11-P41 in the small region 1aa is projected in a reduced ratioon the irradiated region 41a of the wafer 2. An image of the patternelements P13-P43 in the small region 1ab is similarly projected on theirradiated region 41b of the wafer 2. In this image-projectingoperation, a part of the irradiated region 41a and a part of theirradiated region 41b are overlapped so that the image projected on thewafer 2 has the same pattern as the projected pattern 3. Namely, thepattern of the mask 1 shown in FIG. 1B is projected on the wafer 2 suchthat a region 1pa as a part of the small region 1aa and a region 1pb asa part of the small region 1ab are overlapped on the wafer 2 as shown inFIG. 2. If the reduction ratio is 1/4, therefore, the pitch between theirradiation regions 41a and 41b on the wafer 2 should be smaller than1/4 of the pitch between the small regions 1aa and 1ab of the mask 1, bya sum of 1/4 of the width of the boundary region 1b of the mask 1 andthe width of the overlapped portion. To this end, a deflector isprovided for controlling the position of the beam incident upon thewafer 2, so as to control the pitch between the irradiated regions 41a,41b to the value thus determined.

FIG. 7 is a schematic view showing a charged particle beam projectingapparatus in which a charged particle beam BM that has been transmittedthrough the mask 1 passes through a projecting optical system 6consisting of a projecting lens and others, and is then deflected in acontrolled manner by a deflector 7 before the pattern of the mask 1 isprojected in a reduced ratio on the wafer 2.

In the first embodiment as described above, the parting lines d2 areplotted so as not to intersect the pattern elements included in theblock patterns 3ba, 3bb . . . , thereby to prevent the pattern elementsP11, P12 . . . from being split into different small regions when theelements are formed in the respective small regions 1aa, 1ab . . . ofthe mask 1. Thus, the pattern elements P11, P12 . . . are projected onthe wafer 2 without producing connected portions, thereby failure ofdevices caused by connection errors in the pattern can be avoided.Further, the area of each irradiated region of the mask 1 to beirradiated with the charged particle beam having the uniform intensityis set to be larger than the area of each small region 1aa, 1ab . . . ofthe mask 1, so that a pattern in the vicinity of the boundary of thesmall region 1aa, 1ab . . . can be also projected on the wafer 2 withuniform intensity, assuring improved uniformity in the projectedpattern.

While the vertical parting lines are formed in a zigzag pattern as shownin FIG. 1A in the illustrated embodiment, the lateral parting lines maybe plotted in a zigzag pattern so as not to intersect the patternelements if these elements would otherwise lie on the lateral partinglines. It is also possible to form both of the vertical and lateralparting lines in a zigzag pattern.

Second Embodiment

FIG. 3A through FIG. 4A are views explaining the second embodiment ofthe present invention, wherein FIG. 3A shows an example of a pattern 13to be projected that is divided according to a known method, and FIG. 3Bshows an example of pattern 13 that is divided according to a method ofthe present invention. The pattern 13 consists of pattern elements P1,P2, P3 . . . each having a zigzag profile line which has points where adirection of the profile line is suddenly bent, for example right anglecorners in this embodiment, and each of the pattern elements P1, P2, P3. . . extends over a wider range than the range of the region irradiatedwith the charged particle beam. If the projected pattern 13 is routinelydivided into rectangular block patterns 13ca, 13cb . . . , as shown inFIG. 3A, the connection error as described above with respect to thefirst embodiment may occur at some portions of a pattern image projectedon the wafer 2, which portions correspond to divided portions of thepattern elements, such as "A" portion of the pattern element P2, thatare divided by the parting lines d3.

On the other hand, parting lines d4 are plotted in the projected patternof FIG. 3B such that the lines d4 are superposed on portions (such as"B" portion of the pattern element P1) of profile lines of the patternelements P1, P2 . . . at which the width of the pattern elements varies.At singular points of profile lines f1, f2 . . . of the pattern elementsP1, P2 . . . , such as points 5 of the pattern element P2, the edges ofa projected image pattern are rounded due to proximity effects or thelike. Here, the singular point means a point where a direction of lineis suddenly bent to form a zigzag line, for example the right anglecorners 5 shown in FIG. 3B. If the pattern is divided by linesconnecting these singular points as shown in FIG. 3B, therefore, thepattern image projected on the wafer 2 is less likely to have influencesof the connection errors described above, as compared with influences ofthe proximity effects. Namely, the connection errors are less likely tobe observed in the projected pattern image due to the presence of theinfluences of the proximity effects.

In FIG. 4A that corresponds to FIG. 3B, the pattern elements of theblock patterns 13da, 13db (indicated by a hatched area in FIG. 3B) areformed in the small regions 1aa, 1ab of the mask 1, respectively. As inthe first embodiment, the irradiated regions 4a, 4b to be irradiatedwith the charged particle beam having the uniform intensity are definedsuch that the areas of these regions 4a, 4b are larger than those of thesmall regions 1aa, 1ab. FIG. 4B is a view similar to that of FIG. 2,showing irradiated regions at which the wafer 2 is irradiated with thecharged particle beam. As shown in this figure, the wafer 2 isirradiated with the beam such that a part of the irradiated region 41aoverlaps a part of the irradiated region 41b. In the resulting patternimage projected on the wafer 2, a portion of the pattern element P1included in the small region 1aa and another portion of the patternelement P1 included in the small region 1ab are connected to each otherat a connecting portion S1, and in the same manner a portion of thepattern element P2 included in the small region 1aa and another portionof the pattern element P2 included in the small region 1ab are connectedto each other at a connecting portion S2, as shown in FIG. 4B.

While the vertical parting lines are plotted in a zigzag pattern asshown in FIG. 3B so as to pass the singular points on the profile linesof the pattern elements in the second embodiment, the lateral partinglines may also be plotted in a zigzag pattern so as to pass suchsingular points of the profile lines of the pattern elements. It is alsopossible to plot both of the vertical and lateral parting lines in azigzag pattern so as to pass the singular points on the profile lines ofthe pattern elements.

Third Embodiment

FIG. 8A is a view showing a part of a pattern 3 to be projected on awafer of this embodiment. FIG. 8B is a view showing a part of a mask 1.FIG. 8C is a view showing irradiated regions at which the wafer isirradiated with a charged particle beam.

In this embodiment, the pattern 3 is divided into a plurality of blockpatterns by zigzag parting lines in the similar manner to the firstembodiment. When this dividing is performed, in areas where the partinglines can be set, zigzag belt-shaped hatched areas v where any patternelements P11, P12 . . . do not exist are detected as shown in FIG. 8Awith regard to the longitudinal direction. In the same manner,belt-shaped areas u are detected with regard to the lateral direction.Then, parting lines are determined along with these areas. The detectionof these areas can be performed visually by a pattern designer, and itcan also be done by a computer processing with the projected patterndata. When each of the block patterns is formed in a small region of themask 1, an area from the outer profile of the most out pattern elementto the parting line is not formed in the small area, as shown in FIG.8B.

Accordingly, although the width of a portion of the pattern 3 to beprojected corresponding to a portion of the wafer that is irradiated tohave overlapped irradiation is designated with Y2 in the case of thefirst embodiment, the width in this embodiment is designated with Y1which has a smaller value than the Y2, as shown in FIGS. 8A and 8C. As aresult, the size of the mask 1 can be smaller than one of the firstembodiment.

In this embodiment, the areas designated by w, include boundary areas 1bby which the mask 1 is divided into small areas and prohibited areaswhere the block patterns can not be formed at edges of each of smallareas. Accordingly, when the projected pattern is projected on the waferwith this mask, a deflector controls the position of the beam incidentupon the wafer by deflecting the beam with an adjusting amountcorresponding to an amount adding the above mentioned overlapped valueY1 to the value w, in the same manner as the first embodiment.

In this third embodiment, the explanation was done with regard todividing by the zigzag parting lines. However, the idea of thisembodiment can be applied to the case where the projected pattern isdivided by straight parting lines according to a known method.

While the parting lines in the form of zigzag lines that are bent atright angles are employed in the first through third embodiments, theparting lines used in the present invention are not necessarily limitedto the zigzag lines as shown in FIG. 1A and FIG. 3B. For example,step-formed lines, zigzag lines including oblique segments, and curvedlines may be employed depending upon the profiles of the patternelements.

What is claimed is:
 1. A charged particle beam projecting apparatus thatuses a mask used for projecting a pattern, in which (1) a pattern to beprojected on a substrate is divided into a plurality of block patternsby zigzag parting lines in accordance with profiles of pattern elementsof the pattern, (2) the plurality of block patterns are respectivelyformed in a plurality of regions which are arranged at a predeterminedpitch on the mask, and (3) adjacent ones of the plurality of regions, inwhich adjacent ones of the block patterns that are divided by one of thezigzag parting lines are formed, include respective overlapped regionswith which a portion of the substrate is irradiated to have overlappedirradiation, the portion of the substrate corresponding to a portionincluding a zigzag formed portion of the projected pattern divided bythe one of zigzag lines, comprisinga projector that successivelyprojects the plurality of regions of the mask in a reduced ratio ontothe substrate with a charged particle beam; and a deflector thatcontrols deflection of said charged particle beam by an amountcorresponding to the overlapped regions, so that a reduced patternhaving the same shape as the pattern is projected on the substrate.
 2. Acharged particle beam projecting apparatus according to claim 1,whereinsaid charged particle beam is generated so that an area on themask irradiated by the beam that has a uniform intensity is larger thanan area of each of the plurality of regions of the mask.
 3. A chargedparticle projecting apparatus that uses a mask on which a plurality ofblock patterns into which a pattern to be projected on a substrate isdivided are respectively formed in a plurality of regions, comprising:aprojector that successively projects the plurality of regions with acharged particle beam so that the block patterns are successivelyprojected on the substrate, thereby to form a projected pattern on thesubstrate, wherein said charged particle beam is generated so that anarea on the mask irradiated by the beam that has a uniform intensity islarger than an area of each of the plurality of regions of the mask. 4.A charged particle beam projecting apparatus for projecting a pattern ofpattern elements onto a substrate, said apparatus comprising:a maskthrough which a charged particle beam is transmitted and on which thepattern elements are arranged as a plurality of regions, each of saidplurality of regions corresponding to a one of a plurality of blockpatterns into which the pattern to be projected is divided along zigzagparting lines that minimize intersecting of the pattern elements by theparting lines; a projector that successively projects, with the chargedparticle beam, each of the plurality of regions of said mask onto thesubstrate as a reduced ratio image of each region; and a deflector thatcontrols the direction of the charged particle beam which projects theimage of each of the plurality of regions of the mask onto thesubstrate, said projector and said deflector being constructed andarranged so that the respective images of regions of the maskcorresponding to adjacent ones of the plurality of block patternsdivided along a one of the zigzag parting lines partially overlap oneanother to form overlapped images so that a reduced pattern havingreduced pattern elements arranged the same as the pattern elements ofthe pattern to be projected is formed on the substrate.